Again, this won't help your particular situation, and I do not have a
schematic, and lastly, it's an AC motor, but:

My latest (home) sump pump doesn't use float switches, but merely
sensing wires, one high level and one low level.
When water level reaches the tip of the high level wire, the pump is
started, and after the water level drips below the low level wire, an
adjustable timer is started to run the pump for a specified time longer.
Right now, I have the adjustment set for the pump to run about half a minute
after the water drops below both wires.
This way, the back wash down the discharge hose doesn't have volume
enough to start the pump again.
Again, an AC system, and would be simpler to design than your 12 volt
DC situation, but the water just contacting the wires to toggle flip-flop
IC's is a good start at eliminating float switches entirely.
Old Chief Lynn